1. Field of the Invention
The invention relates to classification of wheat varieties as hard or soft wheats. In particular, it relates to a sectioning method for classifying individual wheat kernels as hard or soft.
2. Background Art
Wheat is a major food crop worldwide and is used to produce a wide diversity of baked food products. Wheat varieties are often broadly classified as "hard" or "soft," although other subclasses do exist. Although no definition for the term wheat "hardness" has been universally accepted, this property is important for predicting milling properties and end-uses of wheat varieties. Wheat varieties of similar genetic makeup tend to be suitable for specific products. Hard wheat varieties generally have a harder texture than soft wheats and are genetically different from soft wheats. Hard wheat varieties are used primarily for leavened bread products. For example, bread flour is usually made from hard wheat, largely because of its relatively high protein content and desirable gluten quality. The actual hardness of the wheat is in itself of some significance, however, since hard wheat varieties yield flour of a granular character considered desirable in breadmaking. Hard wheats include hard red winter, hard red spring, and durum. "Soft" flours from soft wheat varieties are preferred for cake and pastry products. Soft wheats include soft red winter, soft white winter, and club. Wheat shipments that contain a mixture of hard and soft wheat varieties are not suitable for either breads or pastries and are either discounted at the marketplace or sold for livestock feed. Therefore, a classification system based on genetic similarities was developed for marketing wheat. Until recently, hard and soft wheat classes were accurately classified by Federal Grain Inspectors using visual methods based on distinct physical characteristics. This is because hard and soft wheats were maintained by breeding programs which preserved the kernel morphology of wheats generally recognized as hard or soft. However, new wheat cultivars have not maintained distinct visual characteristics and are difficult to classify by appearance. Thus, there is a need for an accurate, objective method for classifying wheat kernels to detect lots of wheat where hard and soft varieties have been intermixed along the marketing route. Also, a rapid, accurate method is needed by breeders to classify breeding selections.
Methods which classify hard and soft wheats by means other than physical appearance have been developed. Near infrared reflectance (NIR) spectroscopy which measures wheat hardness based on the scattering of near infrared radiation by ground wheat is becoming the industry standard for differentiating hard and soft wheat samples (AACC Method 39-70, Approved Methods of the American Association of Cereal Chemists (AACC), 8th ed., The Association, St. Paul, Minn. (1983)). However, this and many other methods used for classifying hard and soft wheat varieties use bulk amounts of a wheat sample. Bulk readings give an average value from which to classify a wheat sample. Thus, mixed shipments of wheat that contain mostly hard wheat would still be classified as hard. A single grain method of classifying hard and soft wheats is needed to detect shipments of wheat that have been mixed.
Very few single-grain methods of classifying wheats have been developed. Methods that classify wheat kernels by measuring a physical property of the wheat kernel include measurement of mechanical resistence to penetration (indentation), crushing, or shearing. Katz et al. (Cereal Chemistry 36: 393-401 (1959)) described an indentor which assesses the hardness of individual wheat kernels based on penetration of a spring-loaded stylus into a transverse wheat kernel section prepared with a freezing microtome. Significant variations in hardness within a kernel section were found. The technique was never tested as a means for classifying hard and soft wheat varieties. P. J. Mattern (Cereal Chemistry 65: 312-315 (1988)) described a microscopic method for identification of wheat hardness in single wheat kernels. In this method, wheat kernels are crushed with corrugated rollers and rated from 1 to 10 (soft to hard) on a hardness index established by the researcher, based on the physical characteristics of the fracture surfaces when viewed under a dissecting microscope. While the method accurately classifies hard and soft wheat grains, the technique is labor intensive and not adaptable to automation. Lai et al. (Cereal Chemistry 62: 178-184 (1985)) developed a continuous automatic single-kernel hardness tester which records compression forces (stress) encountered when crushing a wheat kernel as a function of time (strain). A sampling rate of 15 kernels per minute was achieved with this system at a reported accuracy of 90%. It is pointed out by the researchers (see Y. Pomeranz et al., Cereal Chemistry 65: 86-94 (1988)) that with this method, variation in hardness values within a variety may be greater than between varieties. In addition, kernel positioning, degree of kernel shriveling, and kernel geometry affect accuracy. Eckhoff et al. (Cereal Chemistry 65: 503-508 (1988)) developed a single kernel wheat hardness tester which differentiates hard wheat from soft by shearing through a raw kernel and recording the associated breakage curves. The peak force, peak sharpness, and transformation of curve data were used to differentiate samples. The method showed 80% classification accuracy for the five hard and five soft varieties tested. The method is affected by variations in kernel moisture content, size, and orientation during shearing.